1. Field of the Invention
The invention relates to synthetically generated displays and particularly to cathode ray tube displays utilizing stroke writing or raster techniques. The invention also relates to other display technologies such as X-Y plotters.
2. Description of the Prior Art
Synthetically generated displays utilizing, for example, cathode ray tubes (CRT) are known in the art where the display is generated by stroke or calliographic techniques or by raster techniques. A stroke writing CRT display provides synthetic images by deflecting the electron beam so as to draw the shape of the figures to be presented. Raster displays provide an image by generating a pattern of raster scan lines with the image created by illuminating the beam at appropriate points along the raster lines. Vector generation apparatus is utilized in such displays to provide straight line vectors which are concatenated and combined to provide straight or curved line segments of varying positions, directions and lengths to create complex images. The complete display image may be difficult to interpret by a human viewer because of the complexity of the image and because of the close proximity of unrelated symbols or vectors which tend to obscure each other and be confused with one another. For example, complex topographical and tactical maps comprising, for example, roads, rivers, railroads, and designated air spaces and lanes may tend to be difficult to interpret by a viewer.
Interpretation of displayed images may be enhanced by drawing different classes of vectors and lines in a distinguishing manner. The lines may be altered with distinctive dot and dash patterns. For example, lines representing roads may be dashed to distinguish them from lines representing rivers with railroads depicted with a special dashed pattern. Restricted air spaces or air lanes may be further distinguished with other dot and dash patterns. The patterns may comprise any combination of dots, short dashes, long dashes and the like.
In the prior art dashed and dotted lines have been generated by controlling the vector generator to provide a large number of individual concatenated vectors with each dot, each dash and each space requiring a separate vector. The groups of generated vectors are then interpreted by the viewer as dashed or dotted lines.
The prior art method of patterning vectors and lines has several disadvantages. The combined effect of numerous small vectors may not accurately provide the desired total vector direction and length because of round-off or truncation errors associated with each individual small vector. Additionally, the instructions given to the vector generator by the controlling mechanism (such as a microprocessor) are more numerous when generating a plurality of small vectors, thus resulting in the controlling mechanism devoting excessive time and resources to servicing the vector generator. Additionally, a dashed vector in the prior art may take longer to draw than a solid vector because of inefficiencies in initializing numerous vectors.
A vector generator of the type discussed above is described in copending U.S. patent application Ser. No. 354,972, filed Mar. 5, 1982, entitled "Display Vector Generator Utilizing Sine/Cosine Accumulation" by the present inventor and assigned to the assignee of the present application. A stroke writing display of the type discussed above is disclosed in Applicant's Assignee's U.S. Pat. No. 4,115,863, issued Sept. 19, 1978 to Richard R. Brown, entitled "Digital Stroke Display with Vector, Circle and Character Generation Capability". Vector images may also be portrayed utilizing a raster displayed by drawing a vector image into a large memory in which the memory bits correspond to the points, respectively, of the CRT display face. A stroke generator utilizing digital X and Y coordinates may be utilized to write the vector image into the memory by addressing the memory with the X and Y coordinate information and storing the corresponding video at the memory locations. The memory is thereafter addressed by a digital raster generator for providing the CRT video for generating the vector image. A digital raster display generator is disclosed in Applicant's Assignee's U.S. Pat. No. 4,070,662, issued Jan. 24, 1978.